This invention relates to an etchant for use in wet chemical etching of barium-copper-oxygen and calcium-copper-oxygen high-temperature superconductor materials in a process of fabricating elements therefrom. It also relates to a method for chemically etching these materials.
The breakthrough discovery by Bednorz and Muller of superconductivity in the La-Ba-Cu-O system has triggered successive discoveries of many high-temperature superconductors with a transition temperature of above 90.degree. K. It is now expected to apply these Ba-Cu-O high-temperature superconductive materials to various commercially useful forms.
For the device application of these high-temperature superconductive materials, great efforts have been made to fabricate a film therefrom by various dry plating methods including sputtering and electron beam deposition. At the same time, micro-fabrication techniques essential to fabricate elements from high-temperature superconductor films have also been investigated.
The micro-fabrication techniques generally include a lithography technique for making a fine pattern on a resist and an etching technique for transferring the resist pattern to the underlying material. To the former, the lithography which has been established in the semiconductor field is applicable without substantial modification. The latter etching technique must be individually chosen depending on a particular type of material to be treated. No effective etching method has been available partially because only a few years have passed since the discovery of a high-temperature superconductor.
The etching technique includes dry and wet processes. The dry etching process can induce a significant loss of superconductivity, particularly critical superconducting temperature (abbreviated to Tc, hereinafter) when applied to Ba-Cu-O high-temperature superconductors. As to the wet etching process, we already reported a fine patterning process using aqueous phosphoric acid as an etchant for Y-Ba-Cu-O films. Although this wet etching process does not lower the Tc of high-temperature superconductors, it requires a large amount of water for rinsing after etching. Water rinsing creates a serious problem in practice because most Ba-Cu-O systems are hydrolyzable. For example, Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub.7-.delta. system is readily hydrolyzed into CuO, Ba(OH).sub.2 and Y.sub.2 BaCuO.sub.5.
It is therefore desired to develop a technique capable of wet etching high-temperature superconductors without causing the above-mentioned problems.